Mr Gordon argued that the digital economy was a busted flush when it came to growth; Mr Vollrath saw slower growth as a symptom of economic success, a larger services sector and reduced geographic mobility. By presenting solutions, “Restarting the Future” offers a more optimistic vision—as long, that is, as governments follow its advice. Source

Usually "that is" is a shorthand of "that is to say", so can I substitute the latter here? I ask because I feel somehow I can't. I'm seeking for some confirmation.

1 Answer 1


Good point. It would indeed sound unnatural to substitute "that is to say" here.

Sometimes, as you note, "that is" can be replaced by the longer "that is to say." That would be appropriate when what follows "that is to say" is a clarification that doesn't add new information. Often it's just a rephrasing. In the example that you provided, however, "that is" is used in a qualifying clause and at least arguably introduces new information. Another example:

"Of course, we'll be happy to rent an apartment to you, assuming, that is, that there is still availability."

Note that in neither this example nor yours does "that is" introduce a rephrased version of the point being made; rather, it appears in a dependent clause after a word of qualification. The general feeling that I get when I hear this term is not only that a qualification of some sort is to be expected, but that the qualification is such an essential one in relation to the main point that it might perhaps almost go without saying. In that sense, it's similar to "that is to say," in that the information provided afterwards might already be inferred by the listener/reader.


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